33. Scaling Execution: Multi-Worker Parallelism & Device Matrix

Worker Architecture & Test Isolation

- Playwright starts multiple Worker OS processes (e.g. 4 workers on a 4-core CPU). - Each test file runs inside a worker. - Tests within the same file run sequentially by default. - To run tests within a file in parallel: test.describe.configure({ mode: 'parallel' });.

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Cross-Browser Matrix Configuration (playwright.config.ts)

import { defineConfig, devices } from "@playwright/test";
export default defineConfig({
  workers: process.env.CI ? 2 : undefined, // Auto-detect CPUs locally
  projects: [
    {
      name: "Desktop Chrome",
      use: { ...devices["Desktop Chrome"] },
    },
    {
      name: "Desktop Firefox",
      use: { ...devices["Desktop Firefox"] },
    },
    {
      name: "Desktop Safari",
      use: { ...devices["Desktop Safari"] },
    },
    {
      name: "Mobile iPhone 14",
      use: { ...devices["iPhone 14"] },
    },
  ],
});

---

Serial Execution for State-Dependent Workflows

When a small set of tests MUST run in order:

test.describe.serial("Order Processing Pipeline", () => {
  test("create order", async () => { /* ... */ });
  test("process payment", async () => { /* ... */ });
  test("ship order", async () => { /* ... */ });
});